His name isn’t on the ballot, but President Donald Trump’s political clout is on the line in Tuesday’s special election for Senate in Alabama, where polls closed at 8 p.m. Eastern.

Trump and Senate Majority Leader Mitch McConnell have lined up behind Sen. Luther Strange, who was appointed to Attorney General Jeff Sessions’ old seat in February and is running in a crowded GOP primary to complete Sessions’ term. But despite the weighty endorsements, Strange is locked in fierce competition with other Republican hopefuls, including former state Supreme Court Chief Justice Roy Moore, who has led most public surveys of the primary, and Rep. Mo Brooks, who has been running behind Strange in the fight for second place and has hammered the incumbent and McConnell.

If no candidate gets 50 percent of the vote, the top two will advance to a primary runoff on Sept. 26. That’s the expected outcome with 10 candidates dividing the vote, but Strange is leaning hard into Trump’s endorsement to try to make a show of strength in the first round and close in on Moore.

“I think the Trump endorsement is decisive because the election really boils down to who is best suited to help the president implement his agenda,” Strange told POLITICO on Monday. “It’s the agenda he campaigned on and that Alabama voted for. The fact that he has said that I have his support lets the voters know that I’m the person that’s qualified to do that.”

Trump recorded a robocall for Strange’s campaign urging Republicans to vote for him, and Senate Leadership Fund, the super PAC run by McConnell allies, highlighted Trump’s endorsement of Strange in a last-minute ad released Tuesday.

But the super PAC’s main focus has been on preventing Brooks, a firebrand member of the House Freedom Caucus and avowed critic of McConnell, from overtaking Strange and making the top-two primary runoff.

Brooks has not broken 20 percent of the vote in independent polling of the primary, but Strange has also been stuck in mid-to-high 20s in most polls, while Moore has gotten around one-third of the vote. Outspent and out-advertised, Brooks had tried to make waves with attention-seeking ads and statements attacking McConnell, defending Sessions during his recent tiff with Trump, and even highlighting his presence at the shooting that wounded House Majority Whip Steve Scalise and others this summer. (Scalise’s chief of staff criticized that ad.)

Meanwhile, Moore has built up a reliable base of conservative and religious supporters during two stints on the state Supreme Court, which both ended when he was removed for defying federal orders to remove a statue of the Ten Commandments from government grounds and to issue same-sex marriage licenses. His campaign was optimistic ahead of Tuesday that his committed supporters were most likely to turn out for the Senate primary.

“I don’t think the others have quite the mechanism that we have, so we expect to do better than the polls are showing,” said Bill Armistead, a former state Republican Party chairman now chairing Moore’s campaign. “We just don’t know how much better he can do, but we’re trying.”

It’s likely that turnout will be low, said Alabama Republican Party chairwoman Terry Lathan. That could spell trouble for Strange, Brooks or other candidates who draw support from suburban Republicans.

“I guess the question is ‘what message resonates with the voter’ and ‘what voter is motivated to go vote in the middle of August?’” said Lathan, who noted that some voters are on end-of-summer vacations.

Whoever wins the Republican primary will be heavily favored in conservative Alabama, but Democrats have been hoping to make a stronger-than-expected showing in the special election. Former U.S. Attorney Doug Jones has won big-name endorsements from former Vice President Joe Biden and Reps. John Lewis, Cedric Richmond and Terri Sewell, but he faces an obstacle in Robert F. Kennedy Jr., a largely unknown businessman who has a familiar political name, though he is not a member of the famous Kennedy family.

Lathan shrugged off the idea that any Democrat could win statewide in deep red Alabama.

“Look, if you’re going to sign your name up with Chuck Schumer and Nancy Pelosi in the state of Alabama, I don’t care who you are, that’s a problem,” Lathan said.